The present invention relates to a device utilized on a sewing machine for forming a hem on fabric edges.
Attachments of this type for sewing machines are well known in the art; see, for example, DAS [German Published Application] No. 1,097,243. These attachments usually comprise a laterally adjustable ruler guiding the edge of the fabric and means for hem formation arranged in the feeding direction in front of the sewing site, for example, on a base plate. When using such devices, problems are encountered if it is desired to produce especially fine hems on thin, finely woven sewing material. In this connection, it is especially difficult to ensure the straight guidance of the fabric edge to be provided with the hem. In the known devices, the sewing material must be guided by hand through, for example, parallel-walled or conical guide worms around which the passing sewing material is continuously turned, thus forming the hem which is subsequently fixed by means of a sewed seam. In this connection care must be taken that the desired hem width is accurately maintained. This requires great skill, especially in case of fine sewing material.
The present solution makes it possible to flawlessly solve this problem. The device of the present invention is characterized in that a guide shoe is associated with an edge contact surface of a ruler arranged vertically above the base plate. The guide shoe, which acts on the sewing material with a spring force, comprises, in the zone of the edge contact surface, a turndown nose portion arranged in parallel to the contact surface. The turndown nose, in cooperation with a beveled surface of the base plate, extending at an acute angle to the edge contact surface of the ruler, accomplishes the hem formation.
The guide shoe pressing with its underside on the sewing material is suitably suspended to be movable in all directions on a spring arm, the point of engagement of the spring arm with the guide shoe being disposed at a spacing from the ruler in such a way that the pressure surface portions of the guide shoe located on the side of the spring engagement point farther removed from the edge contact surface of the ruler exerts a higher amount of pressure than the pressure surface portion adjacent the ruler. Thus, the escape of the edge of the sewing material from the edge contact surface of the ruler is counteracted so that a flawless, straight guidance of the edge of the sewing material along the ruler is obtained. The turndown nose portion of the guide shoe exhibits a suitable lateral surface, on the side facing away from the ruler, which is parallel to the beveled surface of the base plate, wherein the aforementioned beveled surface constitutes one boundary surface of the edge cutout of the base plate, corresponding to the thickness of the base plate.
The attachment is mounted to the sewing machine so that its base plate covers a portion of the fabric transport lying in front of the needle hole of the machine. If, after the introduction of the sewing material between the base plate and the guide shoe up into the needle hole zone (with the edge of the sewing material being in contact with the contact surface of the ruler) the sewing machine is set into operation, then the transport mechanism pulls the sewing material through the device, wherein, on the one hand, the guide shoe effects a linear contact of the edge of the sewing material against the ruler, whereas the turndown nose of the guide shoe continuously presses the edge of the sewing material downwardly via the beveled surface of the base plate. The edge of the sewing material, thus beveled in this fashion, is turned in under the tension action of the transport mechanism upon leaving the device, and the thus-produced hem is continuously fixed at the sewing site which immediately follows.